Recently, it has become increasingly common for companies based in urban areas to establish a data center at a remote location far from the urban area, and keep various pieces of electronic data produced by its business activity in the data center. The pieces of electronic data are processed, stored, transmitted and received by various servers installed in the data center. In general, for example, as shown in FIG. 6, a rack mount server (hereinafter, referred to just a server) 101 includes a system board 102 on which a baseboard management controller (BMC) 103 is mounted, and the BMC 103 carries out state monitoring of devices and the like included in the server. A server power supply 106 supplies electric power to the BMC 103, and thus, during an interruption of the supply of electric power from the server power supply 106, the BMC 103 does not operate, so that it is difficult to grasp the state of the server. Further, in the case where there is a failure in the server 101 installed at a remote location, a server administrator needs to replace faulty components on site. In this case, when components to be replaced are unknown beforehand, it is necessary to deal with this problem by first identifying components to be replaced on sight and then replacing the relevant components, or replacing the server 101 itself.
Meanwhile, sometimes, there is a case where a spare power supply is reserved in order to make provision for a malfunction of a power supply for the server. However, such a spare power supply needs a depository, and thus increases cost.
In order to deal with these problems, recently, there has been proposed a system which supplies electric power to servers by using a power over Ethernet (PoE) (registered trademark) function.
For example, in Japanese Unexamined Patent Application Publication (JP-A) No. 2006-203730, there has been disclosed a technology for a power receipt terminal device which is provided with a plurality of power sources being each capable of receiving electric power and including a power source receiving electric power through a network cable, and which is capable of supplying a lower-layer power receipt terminal device connected to the power receipt terminal device itself with electric power from a power source which is among the plurality of power sources and which is not used for the power receipt terminal device itself.
Moreover, in Japanese Unexamined Patent Application Publication (JP-A) No. 2010-200279, there has been disclosed an electric power supply control technology for a server, which enables improvement of efficiency of electric power consumed by the server by supplying the server with appropriately selected one of direct-current power supplied from PoE and alternating-current power supplied externally.